This invention relates to a ball head lock nut as a component element of bicycle head parts which cooperate to rotatably support a front fork stem within a head tube of a bicycle frame.
Various models of the bicycle head parts have heretofore been proposed and many of them are currently available in the commercial markets as presented, for example, in "JAPAN'S BICYCLE GUIDE 1982", Vol. 32, Pages 46-53. As apparent from those currently available models, the bicycle head parts are generally assembled in such a manner as illustrated in FIG. 6 of the accompanying drawings.
Referring now to FIG. 6 illustrating a typical prior art construction, a front fork stem (b), which is rigidly connected with a pair of known fork blades (r) by means of a fork crown (f), is inserted into a head tube (a), while a handle stem (HS), which supports a handle bar (HB) at the top as illustrated, is inserted into and fixed to the fork stem (b) by means of an expander cone (EC) which is adjustable by turning an expander bolt (EB). A substantially annular shaped bottom ball head cup (h) is fixedly secured to the lower end of the head tube (a), while a crown cone (g) is fixedly secured to the top side of the fork crown (f). A plural number of steel balls (i), preferably held in a ball retainer (not shown), are interposed for free rotation between the bottom ball head cup (h) and the crown cone (g), so that a lower ball bearing unit (d) consisting of the cooperating three elements (h), (i) and (g) is provided. The lower ball bearing unit (d) serves as a thrust-radial ball bearing.
On the other hand, a substantially annular shaped top ball head cup (j) is fixedly secured to the upper end of the head tube (a), while an internally threaded top cone (m) is mounted by threads on a threaded upper end section (k) of the fork stem (b). A plural number of steel balls (n), preferably held in a ball retainer (not shown), are interposed for free rotation between the top cone (m) and the top ball head cup (j), so that an upper ball bearing unit (c) consisting of the cooperating three elements (m), (n) and (j) is provided. The upper ball bearing unit (c) also serves as a thrust-radial ball bearing.
Thus, the upper and the lower ball bearing units (c) (d) cooperate to support the fork stem (b) together with the handle stem (HS) so as to be relatively rotatable with respect to the head tube (a) which is stationary.
A ball head lock nut (o) is adjustably capped by threads onto the top portion of the threaded upper end section (k) of the fork stem (b) so as to properly depress the top cone (m) in order to prevent the top cone (m) from becoming undesirably loosened or unscrewed.
If desired, one or two locking washers (only one washer (p) is shown in FIG. 6) may be employed. The locking washer (p) is usually formed with a certain rotation preventing means (not shown) in the form of, for example, at least one internal claw or detent projection extending radially inwardly from an inner cylindrical wall thereof, at least one notch formed in the outer cylindrical wall thereof, internal threads engageable with the threaded section (k) of the fork stem (b), serration formed in the lower annular wall of the locking washer for engagement with cooperative serration of the top cone, or combination of selected two of those means as disclosed in the above-referrred "JAPAN'S BICYCLE GUIDE 1982" Vol. 32, Pages 46-53. Thus, when the locking washer (p) is operatively placed between the ball head lock nut (o) and the top cone (m), the washer (p), the lock nut (o) and the top cone (m) cooperate with each other to prevent the top cone (m) from loosening or unscrewing, resulting in that the undesirable loosening in the bearing units (c) and (d) can be prevented to a certain degree.
To prevent the loosening in the bearing units (c) (d) is very important from the viewpoint of durability of the bicycle head parts. In case the bearing units (c) (d) remain loosened, all or some of the bearing surfaces of the top cone (m), the top ball head cup (j), the bottom ball head cup (h) and/or the crown cone (g) are likely to be damaged by beating actions of the steel balls (n) and/or (i) caused by intense vibrations occurring when a bicycle is running on a rough ground surface. Once the bearing surfaces are injured, smooth rotation in the ball bearing units (c) (d) is no longer expected. This disadvantage is especially true with the motocross type bicycles which are used for the bicycle motocross racing now very popular in the United States and some other countries. In the motocross racing, as is well known, a participant has to drive his bicycle on a very rough racing field, and his bicycle is subject to frequent jumps and quick turns.
In particular, when a bicycle jumps up and lands down, such a considerably great impact force or shock is occasionally imparted to the head parts and the head tube via the fork stem, that some of those are momentarily subject to a very slight elastic deformation which causes at the same moment to provide a very narrow gap between the ball head lock nut (o) and the locking washer (p) and/or between the washer (p) and the top cone (m), with the result that the relative and cooperative inter-locking state among the head parts is momentarily released. Therefore, if the fork stem (b) is rotated at this very moment by the cyclist's handle operation, the ball head lock nut (o) is easy to become very slightly loosened. And, if this very slight loosening is repeated, the ball head lock nut (o) becomes more and more loosened, which causes the undesirable loosening in the ball bearing units (c) (d).
It is, therefore, an object of the present invention to provide an improved bicycle ball head lock nut having means for effectively preventing undesirable self-loosening or unscrewing thereof with respect to a threaded upper end section of a bicycle fork stem.
Another object of the invention is to provide an improved bicycle ball head lock nut which is applicable to a motocross type bicycle.
Specifically, the present invention contemplates an improved bicycle ball head lock nut which comprises a split clamping ring disposed within an annular groove formed in a threaded cylindrical internal wall of the ball head lock nut. One or more radially extending threaded through holes are provided each communicated at inner end with the annular groove. A deformable fixing piece which has a diametrically extending slot formed in its inner end wall is disposed within each radially extending threaded through hole, with its diametrically extending slot engaged with the split clamping ring. A set screw screwed into each radially extending threaded through hole is provided until it compresses the fixing piece and makes the same forcibly deformed so as to be tightly engaged with the threads of the radially extending threaded through hole as well as the threads of a threaded upper end section of a fork stem on which the ball head lock nut is capped.